A known ignition system, for example as described in the German patent Publication DE-OS 27 01 967, includes a transducer which generates a speed dependent signal that is fed to a pulse shaping stage and triggers a monostable multivibrator. The multivibrator includes an integrating element or timing element, in particular a capacitor, which is charged from a constant current source during the ignition switch closure time and which is subsequently discharged after the monostable multivibrator is triggered and until such time as the voltage across the capacitor permits the return of the multivibrator into its stable state. The time during which the multivibrator is in its unstable state defines the open period of the ignition control switch. The known ignition system also provides for a parallel conduction path in the monostable multivibrator so as to permit the duty cycle of the transducer to control the on and off times of the ignition at low engine speeds and whenever the voltage across the capacitor exceeds a given level due to prolonged switch closure. While the known system is satisfactory in many instances, it has the disadvantage of generating ignition closure intervals at low rpm whose duration is unnecessarily long and which lead to power losses in the ignition system.